1. Field of the Invention
The present invention relates to a rotation control device of a construction machine, which has a slewing body driven to rotate by a slewing motor (a hydraulic motor), as represented by a hydraulic shovel.
2. Description of the Related Art
In a related art, for example, a rotation system of a hydraulic shovel includes a hydraulic pump supplying a hydraulic fluid to the slewing motor, a control valve controlling charge/discharge of the hydraulic field to/from the slewing motor, rotation operating means for operating the control valve (hereinafter, explained in a case of a general remote-controlled valve), and relief valves respectively provided to a hydraulic fluid path for right rotating and a hydraulic fluid path for left rotating between the slewing motor and the control valve (refer to Japanese Unexamined Patent Application No. 2010-156136).
According to the rotation system, for example, when the remote-controlled valve is operated in a right rotating direction, the hydraulic fluid is supplied to the slewing motor via the hydraulic fluid path for right rotating. Thereby, a slewing body starts rotating in the right direction.
Here, the control valve is configured to block a flow of the hydraulic fluid at a neutral position. Consequently, when the operation of the remote-controlled valve is stopped during the rotation of the slewing body in the right direction and the control valve is returned to the neutral position, the supply of the hydraulic fluid to the slewing motor is stopped, while a decelerating operation is activated to an upper slewing body by operating the relief valve. As a result, the upper slewing body is gradually stopped while being rotated by an inertia thereof.
On the other hand, there is a case of operating the control valve to a left rotating position by operating the remote-controlled valve in a reverse direction for switching to a left rotating operation while decelerating the right rotating operation. Hereinafter, an operation of the remote-controlled valve in a direction the same as the rotating direction is referred to as “forward direction operation”, and an operation of the remote-controlled valve in a direction reverse to the rotating direction is referred to as “backward direction operation”.
Here, a hydraulic shovel which carries out a so-called positive control (hereinafter, referred to as “posicon”) is controlled such that the larger the operating amount of the remote-controlled valve, the larger the capacity of the hydraulic pump is made regardless of the rotating direction of the upper slewing body.
In the posicon, in a case of carrying out the backward operation, the hydraulic fluid of a flow rate in accordance with a magnitude of the operating amount is supplied to a hydraulic fluid path on a discharge side of the slewing motor (hydraulic fluid path for left rotating in the example). The hydraulic fluid is recovered to a tank via the relief valve without being used for accelerating the upper slewing body. Therefore, a loss of a power of the hydraulic pump is brought about in the backward direction operation.